A few years ago I saw acoustician Niels Adelman-Larsen present a new design of acoustic absorber at a scientific conference. His early prototypes were actually air beds. Now, Niels’ has moved on from the camping store, to commercialise the technology, and these absorbers are playing a vital role in ensuring that this year’s Boom Bang-A-Bangs at the Eurovision can be clearly heard.
This year’s Eurovision Song Contest is being held in the enormous, tinpot shipyard in Copenhagen. Left untreated, the sound would rattle around the room for ages creating a muddy sound. The way a sound lingers in a large space is evaluated via the reverberation time, a measure of how long it takes sound to wither away to silence. In a classical concert hall, the reverberation time is typically about 2 seconds, in the Eurovision venue before treatment it was 13 seconds and so completely unsuitable for Hard Rock Hallelujah.
The solution to the acoustics was to bring in stuff that absorb the sound waves, and so speed the decay of the sound. In modern concert halls designed for classical orchestral music, there are often fluffy banners that can be brought into the room to deaden the auditorium when rock bands are playing. But these absorbers usually don’t deal with the bass sound very well, and this is where Niels’ new absorbers come in.
Bass absorbers are often made of a membrane of vinyl vibrating back and forth against a spring created by an enclosed pocket of air. Normally this is a wooden box with a piece of vinyl stuck across the box’s opening. Niels’ innovation was to realise that air beds were very similar. There is a cavity of air and a layer of rubber to vibrate. One of the advantages of the design is that the absorption can be varied by simply inflating or deflating the device.
So when the bands launch into their carefully honed lyrics, such as Scooch’s
Duty free madam?
Yeah, yeah, yeah, yeah.”
You can thank (or not) the new acoustic technology that is making such drivel intelligible.